As is well known, the ultrasonic atomizing apparatus of the type described herein includes ultrasonic vibration generating means having an electric-acoustic transducer and a high frequency oscillator, and an ultrasonic vibrator horn powered by the ultrasonic vibration generating means for atomizing liquid material such as liquid fuel supplied. The spray properties of the ultrasonic vibrator horn such as the flow rate of liquid fuel spray as atomized, the particle size of the atomized droplets, etc. have various effects on the performance of a combusting apparatus incorporating such ultrasonic atomizer. For example, poor spray properties of the ultrasonic vibrator horn may bring forth various troubles such as inability to effect precise control of fuel-air ratio in the combusting apparatus, and worsened combusting conditions which may lead to an increase in the amount of hydrocarbon and carbon monoxide contained in the exhaust gases as well as an increase in the amount of soot produced. In order to eliminate such troubles it is required to improve the atomizing properties of the ultrasonic vibrator horn as described above.
Many attempts have heretofore been made to improve the combusting efficiency by applying ultrasonic vibration to atomize liquid fuel in order to obtain desirable burning conditions in a combustor. However, there are few of the heretofore proposed ultrasonic atomizing devices that have a throughput (say, about 10 cc/sec) sufficient to atomize all of the fuel as supplied to an internal combustion engine in a satisfactory atomizing efficiency without worsening the spray properties as required depending upon the load or the like by a practical size of ultrasonic atomizer. Japanese Patent Public Disclosure No. 37017/1974 to Eric C. Cottell discloses an ultrasonic fuel atomizing apparatus which is intended to be applied primarily to internal combustion engines.
With the apparatus as disclosed in the aforesaid Japanese point a plan public disclosure, however, when applied to an normal combustion engine, it is difficult to atomize a required amount of fuel depending upon changes in load on the engine to finely atomized droplets desirable for combustion in a short time and in large quantities and yet in an effective and efficient manner. Namely, with the Cottell apparatus it is difficult to obtain a great amplitude sufficient for atomizing liquid in large quantities. More specifically, as this apparatus employs a sonic probe formed of a solid member having a large mass, application of such a great amplitude to the sonic probe results in generating too large stresses for materials forming the probe to bear. Furthermore, this apparatus has the disadvantage that it requires a relatively large amount of electric power to atomize the fuel supplied. In the Cornell Apparatus a sonic energy generated by a piezoelectric sonic generator is used to oscillate the sonic probe, the vibrations of the probe being in turn utilized to atomize the fuel supplied to the probe in the atomizing area of the probe. Accordingly when the sonic probe is a solid member having a large mass, as described above, a great amount of sonic energy is required to obtain a great amplitude enough for atomizing the fuel. Hence, a great energy is required to atomize fuel in large quantities. Consequently, the stresses generated in the probe are large to excess, resulting in making it difficult to atomize fuel in large quantities effectively. Moreover, a sonic energy (amplitude energy, for example) transmitted from the piezoelectric sonic generator to the atomizing section of the solid sonic probe to be utilized for atomization of fuel supplied is of substantially the same magnitude as the sonic energy (amplitude energy) initially provided by the piezoelectric sonic generator since the sonic probe is a solid mass, if no account is taken of any attenuation of the energy due to the mass. It cannot thus be said that the sonic energy is utilized effectually and effectively. More particularly, since the amount of energy required to atomize the fuel supplied in the atomizing area of the sonic probe depends upon the effective amplitude of vibration imparted to the fuel fed onto the atomizing section of the sonic probe, as that of the initial sonic energy, as stated above, it cannot be said that the energy from the sonic generator is effectually utilized so as to increase the effective amplitude. The term "effective amplitude" herein used means the amplitude required to atomize liquid, that is, the component of amplitude perpendicular to the plane of the atomizing surface onto which liquid is fed, as expressed by an absolute amplitude X sin .theta. where .theta. is an angle at which the atomizing surface is inclined to the central axis of the horn Accordingly, it is to be noted that the sonic energy from the sonic generator is not utilized effectively and effectually to atomize the fuel to fine droplets, resulting in an increase in the power consumption for atomization of the fuel, as pointed out above.
Further, as the sonic probe is a solid element, the effect of the mass of the probe on attenuation of the sonic energy is unnegligibly large.
In addition, in the Cottell apparatus mentioned above, as a sleeve nozzle is employed, fuel as supplied cascades down the side wall of the sonic probe to the lower atomizing area, so that there is a large surface contact area between the fuel and sonic probe, resulting in a great power loss.
Furthermore, with the Cottell apparatus, a pool of liquid will grow around the outer periphery of the sleeve adjacent its lower end , so that liquid drops from such grown pool to form coarse droplets. It cannot thus be said that the apparatus is capable of completely atomizing a large quantity of fuel to a fine particle size in an effective manner.
It must also be pointed out that with the Cottell apparatus there would often occur misalignment between the sonic probe and the outer sleeve when assembled together. Once such misalignment has occurred, the pattern of spray formed as the fuel is atomized and thrown outwardly is unbalanced, making it difficult to provide uniform desirable burning conditions.